Household Water Filters
as part of the Kitchen Improvement Project
(Cocinas Rurales)
PROMESA – Proecto para el Mejoramiento de la Salud
Valle de Yeguare, Honduras, Central América
An investigative paper by Efrén Gutierrez
August 2004
E. Gutierrez is a second year medical student at
Harvard Medical School, Boston, MA, USA. The
work for this paper was part of his rotation in
Honduras with PROMESA, under the supervision of
Linda Johanna Stern, MPH, Director of PROMESA.
PROMESA is an international health project
operating in Honduras providing primary health
care, training and service learning. PROMESA is
affiliated with Brigham and Women’s Hospital and
Zamorano College.
Introduction
PROMESA is a small international health program that has been working to improve the
conditions in the Yeguare region of Honduras for the past four years. Currently
PROMESA is working on a kitchen improvement project in four small communities (La
Ciénega, Las Tablas, Las Agujas, and Rodeo) in the region. This project’s focus is to
improve the health status of the families by improving the health standards in the kitchen
by offering materials to improve earth stoves, install drains, sinks, install mesh on
windows, and install concrete floors. One improvement that was offered to the families
in the communities was a household size water filtration system to purify contaminated
water. There are a variety of filtration systems; however, it was necessary to find an
inexpensive, functional, and long lasting system. One filter that met those requirements
was the Filtron.
The Filtron is a ceramic filter that is marketed by Potters for Peace and is one method to
decontaminate water that is used for human consumption. The filter works in two ways:
as a filter to remove large contaminants such as protozoa, helminthes, etc., and as a
disinfectant by using colloidal silver to clean the water of potentially harmful bacteria.
The silver is spread on the sides and bottom of the filter. Water passes through the pores
that are formed in the manufacturing process. When the water passes through these pores
it comes in contact with the colloidal silver, which acts as a bactericide. The filter is an
alternative to chlorination, boiling, or using solar energy to decontaminate water (1).
Colloidal silver and function
Silver is a natural metal element that is mined as an ore and can be extracted to form a
pure element. Colloidal silver is a solution where small amounts of silver are suspended
in a liquid, usually water. The colloidal silver solution used in the Filtron is 0.32%
(32,000 ppm) silver Microdyn, a solution of silver dissolved in protein. At high silver
concentrations, a silver colloid solution with water is unstable; therefore a protein
solution is required (1).
Silver has always been used as a disinfectant, and before the introduction of antibiotics,
was given to treat bacterial infections (2, 3). There are three mechanisms by which silver
functions as a disinfectant: reactions with thiol (-SH) groups in bacterial cells, changes to
bacterial cell wall, and inhibiting interactions with nucleic acids. Silver reacts with the
thiol groups found in most bacteria while not interacting with thiol groups in humans.
Various bacterial enzymes use thiol groups and are subsequently inactivated by such
reactions (4). Silver also binds to the bacterial cell wall (5). As it binds, the cell wall
becomes unstable, and the bacteria die. Finally, silver can bind to DNA (the genetic code
for the bacteria) causing structural changes that halt the DNA replication process.
Almost all gastrointestinal bacteria which cause some form of disease are killed by
contact with colloidal silver. (1)
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The colloidal silver is brushed on the sides as well as the bottom of the ceramic filter. In
testing the filter it was discovered that the majority of the filtered water went through the
sides of the filter. Silver is also brushed on both the inside and the outside of the filter.
Some of the silver brushed on the outside seeps into the collection container. The silver
that is within the collection container is necessary to complete the purification process, by
having the silver continue to be in contact with the water (1).
Argyria
Argyria is a condition where the body has been exposed to an excessive amount of silver.
The characteristic feature is the permanent bluish-gray discoloration of the skin which is
benign (1, 6). Silver is absorbed into the skin and may deposit there causing plaques.
Usually argyria begins in the eyes and extremities but then begins to encompass the
whole body. The World Health Organization (WHO) has set the limit of silver exposure
to 10 grams per lifetime (~70 years). The initial disinfected water does have moderate
levels of silver as high as 60μg/L; however these concentrations are below the maximum
acceptable concentration of 100μg/L. In addition, the silver concentration in the filtered
water rapidly decreases after time to levels at 15μg/L. Potters for Peace recommends
discarding the initial filtered water due to its metallic taste. Developing argyria from use
of the Filtron is not likely (1).
Other Contaminants
The filter has been tested with other contaminants such as protozoa, viruses, and arsenic.
Helminthes, protozoa and viruses were tested since they have been associated with
gastrointestinal disease. The elimination of protozoa specifically Giardia lamblia and
Crytosporidium parvum were tested with one filter due to expense of the testing. It was
noted that a reduction of Giardia and Crytosporidium was 99.994% and 99.997%
respectively. Since the pores of the filter range from 0.6-3.0 microns, most Giardia (5-7
microns) and Cryptosporidium (~5 microns) will not pass through (1). Viruses are much
smaller that 3 microns, therefore one test showed that there was no reduction in number
of viruses. Currently there is no role of colloidal silver in deactivating viruses (1).
Arsenic has also been tested due to the interest of people living in Bangladesh where the
water is polluted with arsenic. It was found that approximately 90% of the arsenic was
removed; however this was not enough to prevent arsenic poisoning. No other chemical
compounds have yet been tested (1).
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Maintenance of the filter
In order to maintain the filter, it must be cleaned whenever the rate of filtration drops. If
the filter takes longer than one hour to filter a liter of water, the rate of filtration is too
slow for use. This rate is the minimum allowable flow rate during the manufacturing of
the filter. When it does drop, it means that the filter is clogged and therefore needs to be
scrubbed with a brush.
The recommended cleaning method is:
1) Make sure the clay filter is empty of water
2) Wash hands with soap
3) Remove the clay filter and place on a plate that has been washed with filtered
water.
4) Use clean filtered water to wash the filter. Do not add soap!
5) Scrub the filter both on the inside and outside with a stiff laundry brush to remove
any debris
6) Rise with filtered water until water is clear
Note: Do not use highly concentrated chlorinated water because concentrated
chloride erodes the silver from the filter.
The filtering unit has been found to be functional even after seven years of use. This
indicates that the colloidal silver never “wears out”. However, as a safety precaution,
Potters for Peace recommends either replacing the filter or reapplying colloidal silver
every year (7).
The collecting receptacle should be cleaned once a month to prevent contamination of the
filter.
The following are the recommendations for cleaning the receptacle:
1) Wash hands with soap and filtered water.
2) Remove the clay filtering unit and place on a washed plate.
3) Fill the receptacle one quarter full with water and add two tablespoons of chlorine
bleach.
4) Leave for thirty minutes to disinfect the receptacle.
5) Use this water to wash all of the receptacle and lid with a brush or cloth.
6) If no bleach is available, use soap and filtered water.
7) Rinse the receptacle with boiled or filtered water.
8) Place the clay filter back in receptacle and place the lid on top.
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Concerns regarding the filter
Evaluations of the filter have been conducted in the field that showed a variety of
concerns regarding the management and use of the filters. Certain aspects of the filter
can be problematic; however the studies offer some suggestions. One study showed that
when organizations returned to the communities after distributing the filter and providing
education regarding its maintenance, about half of the filters were broken. A broken
filter should not be used since large cracks may allow bacteria to pass through. To test
whether a filter is broken, one can check the timbre of the filter by hitting it lightly with
the knuckles. Changes in timbre can identify internal cracks that are invisible to the
naked eye. Another identified problem had to do with the faucets. Faucets from the
collecting bins were found to be broken due to misuse. Repairing faucets is difficult
since certain communities may not have access to them. The evaluation studies
recommended buying replacement faucets for the community and educating them on how
to replace the faucets.
For more information about the filter, feel free to contact the following people:
PROMESA
Linda Johanna Stern
Zamorano
Desarrollo y Ambiente
Apdo. 93
Tegucigalpa, Honduras
(504) 776-6140 x2608
ljstern@partners.org
Potters for Peace
P.O. Box 1043
Bisbee, AZ 85603
(520) 432-4616
www.potpaz.org
Honduras
Maximo Andrew
(504) 968-0605
Neighbor (504) 768-3181
km 43 on the road to Choluteca
Honduras
Nicaragua
Ron Rivera
Potters for Peace
Altamira D’Este No. 152 de la Vicky 1c. al lago, 1c arriba
Managua, Nicaragua
(505) 278-8519
filtron2002@yahoo.com.mx; coofice@ibw.com.ni
Ron Rivera: kamaron@ibw.com.ni
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References
1.
Lantagne, Daniele (2001a). Investigation of the Potters for Peace Colloidal Silver
Impregnated Ceramic Filter, Report 1: Field Investigations. Alethia
Environmental.
2.
Basu, S.K, S.R. Deb, and P.S. Aggarwal (1982). Use of Porous Ceramics In
Purification of Water. Glass and Ceramic Bulletin. April-June Volume 29, No. 2.
3.
Russell, A.D. and W.B. Hugo (1994). Antimicrobial Activity and Action of Silver.
Progress in Medicinal Chemistry. Volume 31.
4.
Berger, T.J, J.A. Spadaro, S.E. Chapin, and R.O. Becker (1976). Electrically
Generated Silver Ions: Quantitative Effects on Bacterial and Mammalian Cells.
Antimicrobial Agents and Chemotherapy. Volume 9, Number 2.
5.
Hugo, W.B. (1971). Inhibition and Destruction of the Microbial Cell. Academic
Press, London, New York.
6.
(USEPA) United States Environmental Protection Agency (1996). Integrated Risk
Information System: Silver. http://www.epa.gov/IRIS/subst/0099.html. Accessed
19-8-01.
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ICAITI (Central American Research Institute of Industrial Technology) (1984).
Identification and Evaluation of Design Alternatives for a Low Cost Domestic
Filter for Drinking Water.
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